1. Field of the Invention
The present invention relates to a blood lancet firing device and more particularly relates to a reusable breach loading target pressure activated lancet firing device for penetrating living flesh to provide capillary blood for testing.
2. Description of the Prior Art
It is a common procedure in hospitals, clinics and doctor's offices to perform tests on blood provided by cutting or puncturing the skin and causing the capillaries of the patient to bleed. It is also common for persons afflicted with diabetes mellitus to frequently test their own capillary blood to determine blood glucose levels. The instrument used to cut the capillaries is called a lancet. The lancet typically includes a shank portion, which is formed to facilitate holding the lancet, and a sharp cutting portion. A lancet of this type, wherein the cutting portion is planar and V-shaped, is shown in U.S. Pat. No. 3,046,987 to Ehrlich. Another lancet design is shown in U.S. Pat. No. 3,358,689 to Higgins.
There is a certain amount of pain associated with producing capillary blood with a lancet since the skin at the patient's finger tips, which contains sensitive nerve endings, is severed to obtain the blood sample. Patient discomfort and apprehension are magnified by the sight of the lancet as it is thrust toward the skin by the doctor or nurse. These problems exist to a greater degree when the patient obtains his own blood sample since it is psychologically difficult to prick one's own finger tip with a lancet. Finger pricking with a hand held lancet can cause additional pain if the lancet is not thrust straight into and out of the patient. If the lancet cutting tip enters angularly or is moved while inside the patient, additional slicing and irritation of nerve endings will result. Also, pain from lancet finger pricks is reduced if the lancet is quickly removed from the patient's finger.
Automatic lancet devices offer improvements regarding some of the above mentioned physical and psychological problems in that they automatically propel the lancet tip into and out of the patient. U.S. Pat. No. 4,230,118 to Holman et al. teaches a reusable automatic lancet device which includes a disposable mounted needle to perform the lancet function. The Holman et al. device has a spring driven arm which is pivoted at one end in a housing while its other end protrudes through an arcuate slot in the housing. The mounted needle is placed in a holder portion at the end of the arm so that the needle is positioned tangentially to the arcuate slot. The arm may then be rotated clockwise to engage a latch. Approximately 90.degree. in a counterclockwise direction from the latch is a finger rest with a hole therein. When the patient's finger is placed against the finger rest covering the hole and a trigger is deflected, the arm drives the needle through the arcuate path causing the needle to enter the hole in the finger rest, penetrate the finger and then become withdrawn.
The Holman et al. automatic lancet device has several deficiencies. Most noteworthy is that when the mounted needle is loaded into the arm, the needle is facing the user's hand. This front loading procedure offers the potential for contamination of the needle point and accidental skin puncture during loading and unloading of the lancet. Also, the needle in the Holman et al. device travels in an arcuate path and therefore enters the skin at an angle, slicing through the skin, rather than entering straight in along its longitudinal axis. Further, it is believed that the separate operation of pressing the trigger tends to set the lancet device in motion further adding to the potential for slicing motions while the needle is in the patient's skin. Finally, the lancet's motion toward the patients skin is still visible.
Another automatic lancet device is manufactured in West Germany and sold in the United States under the trade name AUTOCLIX, by BIO-DYNAMICS Company of Indianapolis, Ind. The AUTOCLIX device works with a disposable lancet similar to that described in the aforementioned patent to Higgins. The AUTOCLIX device is a relatively large rectangular structure with rounded corners which is held in the user's hand so that an external plunger is manipulable by the thumb while the end with a pressure platform projects outwardly from the other side of the user's hand. In use, the plunger is depressed to load the spring mechanism and to allow the front loading insertion of a lancet, with protective tip installed, through a hole in the pressure platform. The tip is then removed to expose the sharp lancet point and the plunger released to retract the lancet into the structure. Placing the patient's finger tip over the pressure platform hole and applying force on the pressure platform, with that finger, will activate the device causing the lancet point to momentarily protrude through a hole in the pressure platform penetrate the finger tip and to retract therefrom. After use, the plunger is again pressed causing the sharp lancet point to protrude from the pressure platform hole and to be ejected if the point is directed downwardly. The lancet tip should then be reinstalled over the lancet point.
Although complex in structure, the AUTOCLIX device offers the advantage of target pressure activation, i.e., the finger which will be pierced by the lancet point provides the force to activate the firing mechanism. Target pressure activation is desirable in a lancet device where the lancet point moves into and out of the user's flesh in a straight line, rather than in an arcuate path as provided by Holman et al., because the activation forces are in a direction which is approximately parallel to the motion of the lancet and these forces have less tendency to produce a tilting or twisting of the lancet device while the lancet is in motion and therefore reduces the potential for slicing action by the lancet point while it is in the user's finger. Also, the AUTOCLIX device shields the lancet motion from the patient's view. However, this lancet device still has deficiencies in that it must be front loaded thus exposing the lancet tip to accidental contamination and the user to accidental skin puncture. In addition, this device fires regardless if there is a lancet installed or not.
U.S. Pat. No. 4,416,279 to Lindner et al. teaches a lancet device which allows breach loading of the lancet into a lancet holding member. The Lindner et al. device is grasped by the user so that it is held between the thumb and the finger to be penetrated by the lancet. In use, the user, with his free hand, rotates an operating cylinder, which is concentric with the main body of the device, until the lancet holding member retracts to a low position where the lancet may be installed. Movement of the lancet holding member is caused by a guide pin or follower which is connected to the lancet holding member and rides on a cam path within the operating cylinder. Movement of the follower along the cam path also compresses a drive spring. After lancet installation, further rotation of this operating cylinder causes further compression of the drive spring. Compression of the drive spring continues until the cam path abruptly ends and the lancet holding member is propelled toward the user's finger. Although the Lindner et al. device offers the advantage of breach loading, it still is deficient in that motion of the lancet or structure associated with the lancet is visible to the user. Also, activation of the Lindner et al. device via twisting of the operating cylinder makes it difficult to maintain a constant positional relationship between the device and the user's finger. Accordingly, this twist activation is believed to add to the potential for slicing motions while the lancet point is in the patient's skin.
Although various forms of automatic lancet devices have been addressed by the prior art, there is still a need for a simple, straight-forward, easily fabricated reusable lancet firing device which is breach loading, target pressure activated and which propels the lancet point straight into and out of the patient's flesh. It is also desirable to provide a lancet firing device with structure to shield the motion of the lancet from the patient's view.